The primate visual cortex is the end station for the reception, integration and perception of visual impulses. There are at least half a dozen cortical areas devoted to visual processing, yet our knowledge concerning the structural and functional organization of the visual cortex has gone little beyond that of the striate cortex. The prestriate cortex or area 18 almost completely surrounds the striate cortex, and represents a "second order of transformation" of the visual hemifield. Among its cortical and subcortical inputs are two major afferents, one from the striate cortex and one from the pulvinar. The former pathway is suggestive of a serial type of visual processing, while the latter represents a thalamocortical channel that may function in parallel with the geniculostriate pathway. Since the striate afferents end in regularly-spaced columns, with the densest distribution in lamina IV, and pulvinar afferents end in pathces mainly in laminae IV or III, we wish to determine whether these two sets of inputs actually superimpose or alternately interdigitate with each other in laminae III and IV of the prestriate cortex. By double labelling these afferents, one with lesion-degeneration and the other with 3H-amino acids, we can estimate their spatial relationship with each other at the light microscopic level. At the electron microscopic level, the differentially labelled afferents can be traced serially to determine if they had independent or overlapping synaptic domains, if they synapse in the same or different lamina(e), and if they converge on the same cell. The types and prevalence of synapses each afferent system makes can also be determined. Combined degeneration and Golgi techniques will also be employed to establish whether specific afferents (either pulvinar or striate, marked by degeneration) end on the same or different types of neurons (identified by Golgi impregnation). By establishing the anatomical basis for functional circuitries, we may gain better understanding of how visual integration is achieved within the prestriate cortex.